The present invention relates to a scanning atomic force microscope for observing the topography of a specimen surface by making use of an atomic force exerted between substances.
The prior art scanning atomic force microscope uses a probe comprising a cantilever and a probe portion formed over the cantilever which is made of silicon nitride or silicon. The atomic force exerted between the probe portion and the specimen surface is detected as a deflection of the cantilever, a change in the amplitude of the vibration, or a change in the resonance frequency. The probe tip and the specimen are moved relative to each other while maintaining the distance between them constant. Thus, the specimen surface is observed. In this case it is common practice to utilize an optical procedure, for detecting the displacement of the cantilever. Where such an optical procedure is employed, the instrumentation is complicated. Furthermore, various adjustments such as adjustment of the optic axis are necessary. Hence, it has been complex and laborious to handle the instrument.
In connection with them, a cantilever incorporating a piezoelectric detection mechanism for electrically detecting vibrations is described in Japanese Patent Unexamined Publication No. 196458/1993. Also, AFM (atomic force microscope) probes using quartz oscillators have been proposed in Japanese Patent Unexamined Publication Nos. 309803/1988 and 102008/1992.
In the case of the above-cited Japanese Patent Unexamined Publication No. 196458/1993 where displacements of the cantilever are electrically detected without using any optical procedure, a process for forming a thin piezoelectric film is involved. Therefore, the fabrication of the probe is complicated.
In the quartz oscillator probe described in the Japanese Patent Unexamined Publication No. 309803/1988, the quartz oscillator adheres to the probe portion together. This structure is not easy to manufacture. The quartz oscillator probe described in the Japanese Patent Unexamined Publication No. 102008/1992 is not associated with electrical detection. Moreover, no detailed description is made of the fabrication. Accordingly, a method of easily fabricating an atomic force microscope (AFM) probe using a quartz oscillator and a scanning atomic force microscope which is easy to handle have been sought for.
Furthermore, in the AFM probe, sharpening of the probe tip presents problems. Accordingly, it is an important object to provide a method of sharpening the tip.
It is an object of the invention to provide an apparatus of AFM that has simple structure and has a no necessity of adjusting the optic axis.
Another object of the invention is to provide a method for forming easily a probe for AFM.
A further object of the invention is to provide a method for sharpening a tip of a probe for AFM.
To attain the above objects, an atomic force microscope (AFM) probe is comprised of a probe portion made of quartz and a cantilever portion made of the same quartz as the probe portion. The probe portion has a tip which is formed as the intersecting point, or vertex, of three planes including at least two crystal planes. Electrodes for electrically detecting deflections of the cantilever are formed thereon. This AFM probe is fabricated by a method consisting, for example, of exposing a resist, using a cantilever mask and a probe mask, and performing an etching process, based on a pattern obtained by the exposure. The cantilever mask is placed in position in the Y direction relative to a quartz base plate or substrate lying in the Z-plane. The probe mask is placed in position in the X direction relative to the quartz substrate and subtends an angle not exceeding the angle that two crystal planes make to the substrate.
The invention also provides an AFM probe comprising a cantilever and a probe portion having a tip extending in the X direction. The probe tip assumes a pyramidal form and has been sharpened by isotropic etching. The cantilever is formed over a quartz substrate lying in the Z-plane and extends in the Y direction. This AFM probe can be fabricated, for example, by performing exposure of resist, using a cantilever mask and a probe mask, and performing an etching process, based on a pattern obtained by the exposure. The cantilever mask is formed over the quartz substrate and extends in the Y direction. The probe mask is shaped like a belt and extends in the X direction.
In addition, the present invention provides a scanning atomic force microscope comprising: any one of these AFM probes; a vibrating means for vibrating a piezoelectric body at its resonant frequency; a means for detecting changes in resonance characteristics of the probe as changes in electrical characteristics, said changes in resonance characteristics being caused by an atomic force exerted between the tip of the probe and a surface of said specimen; a control means for maintaining constant the space between the probe tip and the surface of the specimen according to the output signal from the detecting means; and a scanning means for observing topography of the surface of the specimen.